1. Field of the Invention
This invention relates generally to the distribution of video and interactive services. More particularly, this invention relates to subscriber stations for receiving digital video programs and supporting interactive services.
2. Description of the Background Art
Distribution of digital video programs via cable television systems or direct broadcast satellite (DBS) is becoming increasingly popular. In addition, distribution of interactive services such as video on-demand services and Internet (including World Wide Web) access is also becoming increasingly popular.
Many homes now have a subscriber station or terminal that provides access to digital video programming. The subscriber station is typically in the form of a stand-alone set-top box. The stand-alone set-top box receives signals over a cable system, a direct broadcast system, or other distribution system. Of particular significance, the stand-alone set-top box supports only a single television (or monitor or other display-device). If a user wants to support another television (or monitor or other display device), then a second stand-alone set-top box is typically required. Moreover, if the user wants to support a third television (or monitor or other display device), then a third stand-alone set-top box is typically required. And so on for additional televisions. The need for multiple identical stand-alone set-top boxes to support multiple televisions is significant extra cost to the user and/or the service provider.
The present invention overcomes the above-described disadvantages by providing a master subscriber station that supports a relatively low cost slave subscriber station. The slave subscriber station relies upon the master subscriber station for certain functions and therefore can be implemented as a lower cost design. Duplication of functionality is therefore minimized, resulting in lower complexity and lower overall costs.
One distinction of the master subscriber station over a conventional stand-alone set-top box is the master subscriber station""s ability to process multiple video streams such that one or more of the additional streams can be sent via coaxial cabling to a slave subscriber station. Another distinction is the master subscriber station""s ability to receive and process control signals from the slave subscriber station. In a preferred embodiment of the present invention, the master subscriber station can also function as a stand-alone unit with minimal modifications.
One distinction of the slave subscriber station over a conventional stand-alone set-top box is the slave subscriber station""s ability to receive and demodulate video and audio streams sent by the master subscriber station. Another distinction is the slave subscriber station""s ability to send remote control commands back to the master subscriber station over the same coaxial cable that delivers the video streams to the slave subscriber station. For example, in a video-on-demand (VOD) application, the slave subscriber station may send a command indicating a movie selection to the master subscriber station. As another example, in a digital video broadcast application, the slave subscriber station may send a command indicating that a broadcast channel selection to the master subscriber station.
In a preferred embodiment of the present invention, the slave subscriber station includes a relatively low-speed RF (radio frequency) modem (modulator/demodulator) to communicate with the master unit. This allows the slave subscriber station to be of substantially reduced cost and complexity because a substantial portion of the cost and complexity of a conventional stand alone set-top box lies in the RF tuner, IF (intermediate frequency) amplifier, and QAM demodulator circuitry. Also, in a preferred embodiment of the present invention, the slave subscriber station is housed in a small, inexpensive enclosure and uses a wall transformer to supply power.
In a preferred embodiment of the present invention; advantage is taken of the fact that the digital bit rate of a single video program (e.g., a movie) which is compressed according the MPEG (motion picture expert group) standard can be as low as 1.544 megabits per second (Mb/s), whereas the digital bit rate capacity of a standard 6 megahertz (MHz) analog CATV channel can be as high as 27 Mb/s for 64 QAM (quadrature amplitude modulation) and as high as 38.8 Mb/s for 256 QAM. The relatively large digital bandwidth of the standard analog CATV channel allows several digital MPEG channels to be packaged and transmitted within a single standard analog. CATV channel.
Unlike a conventional stand-alone digital set-top box which selects and demultiplexes only one MPEG digital channel at any one time, the master subscriber station is able to select and demultiplex multiple MPEG digital channels at any one time. One digital channel may be displayed on a television coupled to the master subscriber station, and a different (or the same) digital channel may be displayed on each of the slave subscriber stations. Furthermore, a second master subscriber station (possibly in a different residence in the same neighborhood) tuned to the same 6 MHz CATV channel as the first master-set top box mentioned above would be able to select and demultiplex different (or the same) digital channels as the first master subscriber station.
These and other features and advantages of the present invention may be better understood by considering the following detailed description of a preferred embodiment of the invention. In the course of this description, reference will frequently be made to the attached drawings.